Sorry, did a bit of a post and run yesterday. Thank you all for responding. I think I see what you are saying about the difference between -- well, I guess for lack of a better term, "objectively flattering" (looks good to everyone) versus "subjectively flattering" (appealing to the wearer for personal reasons, despite deviating from the standard).
I guess I'm still wondering, however, if there really is such a thing as an objectively flattering look. In other words, can certain clothes really look good to *everyone*? We are not all attracted to exactly the same thing. I mean, I think it's true that the generally favoured silhouette, in this place and time at least, seems to be the shapely, slender hourglass, and clothes that are considered flattering are ones that make us approximate that shape (if we aren't already that shape). I myself tend to shy away from clothing that makes me appear blockier, heavier, or too straight through the middle. But one person's idea of the perfect hourglass might be someone else's idea of too boyish, right?
Back to the boyfriend jeans. In the case of baggy boyfriend jeans, I guess they're considered "not flattering" because they obscure the curves of a woman's bottom, and make her appear less shapely. But I personally prefer a less shapely, more androgynous look. I'm always trying to downplay my bust and I'm not usually drawn to clothing that looks va-va-voom (although I can appreciate the look on others), which explains why I like the look of baggy jeans so much. They "slenderize the hourglass", to more closely approximate my own personal preference.
I'm having trouble putting my ideas into words this morning.